Thin-layer-covered golf ball with improved velocity

ABSTRACT

Golf balls including centers formed from polybutadiene reaction products having a percent change in dynamic stiffness from 0° C. to −50° C. of less than 130 percent where the reaction products include a resilient polymer component, a crosslinking material, a cis-to-trans catalyst, and a free radical source. The golf balls may be formed with polyurethane covers, covers formed from castable reactive liquid materials, among other materials. The golf balls may also include an intermediate layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/434,131, filed May 16, 2006, now pending, which is a continuation ofU.S. patent application Ser. No. 10/828,253, filed Apr. 21, 2004, nowU.S. Pat. No. 7,105,610, which is a divisional of U.S. patentapplication Ser. No. 10/256,011, filed Sep. 27, 2002, now U.S. Pat. No.6,818,705, which is a continuation of U.S. patent application Ser. No.09/721,740, filed Nov. 27, 2000, now U.S. Pat. No. 6,486,261, which is acontinuation-in-part of U.S. patent application Ser. No. 09/461,736,filed Dec. 16, 1999, which claims the benefit of U.S. Patent ProvisionalApplication No. 60/113,949, filed Dec. 24, 1998, and acontinuation-in-part of U.S. patent application Ser. No. 09/311,591,filed May 14, 1999, now U.S. Pat. No. 6,210,294, and also acontinuation-in-part of U.S. patent application Ser. No. 09/274,015,filed Mar. 22, 1999.

FIELD OF THE INVENTION

The invention relates generally to golf balls and, more specifically, togolf balls with covers formed of a polymer blend comprising apolyurethane composition and cores formed of a polybutadienecomposition. The polyurethane composition comprises a prepolymer of apolyisocyanate and a polyol, and a diamine curing agent. Thepolybutadiene composition comprises a butadiene polymer with aresilience index greater than about 40 and a molecular greater thanabout 200,000. The golf balls of the present invention have been foundto provide improved velocity.

BACKGROUND OF THE INVENTION

Conventional golf balls can be divided into several general classes: (a)solid golf balls having one or more layers, and (b) wound golf balls.Solid golf balls include one-piece balls, which are easy to constructand relatively inexpensive, but have poor playing characteristics andare thus generally limited for use as range balls. Two-piece balls areconstructed with a generally solid core and a cover and are generallythe most popular with recreational golfers because they are very durableand provide maximum distance. Balls having a two-piece construction arecommonly formed of a polymeric core encased by a cover. Typically, thecore is formed from polybutadiene that is chemically crosslinked withzinc diacrylate and/or other similar crosslinking agents. These ballsare generally easy to manufacture, but are regarded as having limitedplaying characteristics. Solid golf balls also include multi-layer golfballs that are comprised of a solid core of one or more layers and/or acover of one or more layers. These balls are regarded as having anextended range of playing characteristics.

Wound golf balls are generally preferred by many players due to theirhigh spin and soft “feel” characteristics. Wound golf balls typicallyinclude a solid, hollow, or fluid-filled center, surrounded by atensioned elastomeric material and a cover. Wound balls generally aremore difficult and expensive to manufacture than solid two-piece balls.

A variety of golf balls have been designed by manufacturers to provide awide range of playing characteristics, such as compression, velocity,“feel,” and spin. These characteristics can be optimized for variousplaying abilities. One of the most common components that manufacturershave addresses for optimizing and/or altering the playingcharacteristics of golf balls, is the polymer components present inmodern golf ball construction, in particular, golf ball centers and/orcore. In addition to ionomers, one of the most common polymers employedis polybutadiene and, more specifically, polybutadiene having a highcis-isomer concentration.

The use of a polybutadiene having a high cis-concentration results in avery resilient and rigid golf ball, especially when coupled with a hardcover material. These highly resilient golf balls have a relatively hard“feel” when struck by a club. Soft “feel” golf balls constructed with ahigh cis-polybutadiene have low resilience. In an effort to provideimproved golf balls, various other polybutadiene formulations have beenprepared, as discussed below.

U.S. Pat. No. 3,239,228 discloses a solid golf ball having a core moldedof polybutadiene rubber with a high sulfur content, and a cover. Thepolybutadiene content of the core is stereo-controlled to theconfiguration 25-100 percent cis- and 0-65 percenttrans-1,4-polybutadiene, with any remainder having a vinyl configurationof polybutadiene. A preferred embodiment of the polybutadiene golf ballcore contains 35 percent cis-, 52 percent trans-, and 13 percentvinyl-polybutadiene. The level of trans- and vinyl-content are disclosedto be unimportant to the overall playing characteristics of the polymerblend.

British Patent No. 1,168,609 discloses a molding composition from whichimproved golf ball cores can be molded and which containscis-polybutadiene as a basic polymer component. The core polymercomponent typically includes at least 60 percent cis-polybutadiene, withthe remainder being either the trans- or vinyl-forms of polybutadiene.In a preferred embodiment, the core polybutadiene component contains 90percent cis-configuration, with the remaining 10 percent being eitherthe trans- or vinyl-configurations of 1,4-polybutadiene.

U.S. Pat. Nos. 3,572,721 and 3,572,722 disclose a solid, one- ortwo-piece golf ball, with the two-piece ball having a core and a cover.The cover material can include any one of a number of materials, orblends thereof, known to those of ordinary skill in the art, includingtrans-polybutadiene which may be present in an amount from at least 90percent, with the remainder being the cis- and/or vinyl configuration.

British Patent No. 1,209,032 discloses a two- or three-piece golf ballhaving a core and a cover. The core or cover material can be anymaterial capable of being crosslinked. In particular, the material canbe a polymer or a copolymer of butadiene or isoprene. Preferably, thepolymer component is polybutadiene having a cis content of greater than50 percent by weight.

U.S. Pat. No. 3,992,014 discloses a one-piece, solid golf ball. The golfball material is typically polybutadiene, with a stereo-configurationselected to be at least 60 percent cis-polybutadiene, with the remaining40 percent being the trans-polybutadiene and/or1,2-polybutadiene(vinyl)isomers.

U.S. Pat. No. 4,692,497 discloses a golf ball and material thereofformed by curing a diene polymer including polybutadiene and a metalsalt of an alpha, beta ethylenically unsaturated acid using at least twofree radical initiators.

U.S. Pat. No. 4,931,376 discloses a process for producing butadienepolymers for use in various applications, including golf ball covermaterials. One embodiment of the invention employs a blended polymericresin material, including at least 30 percent by weight of atrans-polybutadiene polymer as a golf ball cover on a two-piece ball. Ina preferred embodiment, the golf ball cover material contains a blendincluding 30 to 90 percent by weight of a trans-polybutadiene polymer.

U.S. Pat. No. 4,971,329 discloses a solid golf ball made from apolybutadiene admixture of cis-1,4 polybutadiene and 1,2 polybutadiene,a metal salt of an unsaturated carboxylic acid, an inorganic filler, anda free radical initiator. The admixture has about 99.5 percent to about95 percent by weight of cis-1,4 polybutadiene and about 0.5 percent toabout 5 percent by weight of 1,2 polybutadiene.

U.S. Pat. No. 5,252,652 discloses a one-piece or multi-layered golf ballcore with improved flying performance from a rubber compositioncomprising a base rubber, preferably 1,4-polybutadiene with acis-content of at least 40 mole percent, an unsaturated carboxylic acidmetal salt, an organic peroxide, and an organic sulfur compound and/or ametal salt thereof. The organic sulfur compound and/or a metal salt istypically present in an amount from about 0.05 to 2 parts per hundred byweight and the organic peroxide is typically present in an amount fromabout 0.5 to 3 parts per hundred by weight of the total polymercomponent.

European Patent No. 0 577 058 discloses a golf ball containing a coreand a cover that is formed as two separate layers. The inner layer ofthe cover is molded over the core and is formed from ionomer resin. Theouter layer of the cover is molded over the inner layer and is formedfrom a blend of natural or synthetic balata and a crosslinkableelastomer, such as polybutadiene. In one embodiment of the outer layerof the cover, the elastomer is 1,4-polybutadiene having a cis-structureof at least 40 percent, with the remaining 60 percent being thetrans-isomer. A preferred embodiment contains a cis-structure of atleast 90 percent and more preferably, a cis-structure of at least 95percent.

U.S. Pat. No. 5,421,580 discloses a wound golf ball having a liquidcenter contained in a center bag, a rubber thread layer formed on theliquid center, and a cover over the wound layer and liquid center. Thecover material can include any one of a number of materials, or blendsthereof, known to those of ordinary skill in the art, includingtrans-polybutadiene and/or 1,2-polybutadiene(vinyl), such that the coverhas a JIS-C hardness of 70-85; preferred trans-percentages are notdisclosed.

U.S. Pat. No. 5,697,856 discloses a solid golf ball having a core and acover wherein the core is produced by vulcanizing a base rubbercomposition containing a butadiene rubber having a cis-polybutadienestructure content of not less than 90 percent before vulcanization. Theamount of trans-polybutadiene structure present after vulcanization is10 to 30 percent, as amounts over 30 percent are alleged todetrimentally result in cores that are too soft with deterioratedresilience performance, and to cause a decrease in golf ballperformance. The core includes a vulcanizing agent, a filler, an organicperoxide, and an organosulfur compound.

British Patent No. 2,321,021 discloses a solid golf ball having a coreand a cover formed on the core and having a two-layered coverconstruction having an inner cover layer and an outer cover layer. Theouter cover layer is comprised of a rubber composite that contains 0.05to 5 parts by weight of an organic sulfide compound. The core rubbercomposition comprises a base rubber, preferably 1,4-polybutadiene havinga cis-content of at least 40 percent by weight, a crosslinking agent, aco-crosslinking agent, an organic sulfide, and a filler. Thecrosslinking agent is typically an organic peroxide present in an amountfrom 0.3 to 5.0 parts by weight and the co-crosslinking agent istypically a metal salt of an unsaturated fatty acid present in an amountfrom 10 to 40 parts by weight. The organic sulfide compound is typicallypresent from 0.05 to 5 parts by weight.

U.S. Pat. No. 5,816,944 discloses a solid golf ball having a core and acover wherein the core has a JIS-C hardness of 50 to 80 and the coverhas a Shore-D hardness of 50 to 60. The core material includesvulcanized rubber, such as cis-polybutadiene, with a crosslinker, anorganic peroxide, an organosulfur compound and/or a metal-containingorganosulfur compound, and a filler.

Additionally, conventional polymers that have a high percentage of thetrans-polybutadiene conformation, such as DIENE 35NF, from FirestoneCorp., that has 40 percent cis-isomer and 50 percent trans-polybutadieneisomer, and mixtures of high-cis- and high-trans-polybutadiene isomers,such as CARIFLEX BR1220, from Shell Corporation, and FUREN 88, fromAsahi Chemical Co., respectively, typically do not yield high resiliencevalues and therefore are not desirable.

In addition to changing center or core ingredients to affect golf ballperformance characteristics, a number of patents have issued that aredirected towards modifying the properties of layers and covers used informing a variety of golf balls, such as wound balls, conventional solidballs, multi-layer balls having dual cover layers, dual core layers,and/or balls having a mantle layer disposed between the cover and thecore. The most common polymers used by manufacturers in golf ball layersand covers have been ionomers, such as SURLYN, commercially availablefrom E.I. DuPont de Nemours and Co., of Wilmington, Del. Recently,however, manufacturers have investigated the used of alternativepolymers, such as polyurethane. For example, U.S. Pat. No. 3,147,324 isdirected to a method of making a golf ball having a polyurethane cover.

Polyurethanes have been recognized as useful materials for golf ballcovers since about 1960. Polyurethane is the product of a reactionbetween a polyurethane prepolymer and a curing agent. The polyurethaneprepolymer is a product formed by a reaction between a polyol and adiisocyanate. The curing agents used previously are typically diaminesor glycols. A catalyst is often employed to promote the reaction betweenthe curing agent and the polyurethane prepolymer.

Since 1960, various companies have investigated the usefulness ofpolyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061teaches a golf ball made from a polyurethane prepolymer of polyether anda curing agent, such as a trifunctional polyol, a tetrafunctionalpolyol, or a diamine. U.S. Pat. No. 5,334,673 discloses the use of twocategories of polyurethane available on the market, i.e., thermoset andthermoplastic polyurethanes, for forming golf ball covers and, inparticular, thermoset polyurethane covered golf balls made from acomposition of polyurethane prepolymer and a slow-reacting amine curingagent, and/or a difunctional glycol. The first commercially successfulpolyurethane covered golf ball was the Titleist® Professional ball,first released in 1993.

Unlike SURLYN® or ionomer-covered golf balls, polyurethane golf ballcovers can be formulated to possess the soft “feel” of balata coveredgolf balls. However, golf ball covers made from polyurethane have not,to date, fully matched SURLYN®-covered golf balls with respect toresilience or the rebound that is a function of the initial velocity ofa golf ball after impact with a golf club.

U.S. Pat. No. 3,989,568 discloses a three-component system employingeither one or two polyurethane prepolymers and one or two polyols orfast-reacting diamine curing agents. The reactants chosen for the systemmust have different rates of reactions within two or more competingreactions.

U.S. Pat. No. 4,123,061 discloses a golf ball made from a polyurethaneprepolymer of polyether and a curing agent, such as a trifunctionalpolyol, a tetrafunctional polyol, or a fast-reacting diamine curingagent.

U.S. Pat. No. 5,334,673 discloses a golf ball cover made from acomposition of a polyurethane prepolymer and a slow-reacting polyaminecuring agent and/or a difunctional glycol. Resultant golf balls arefound to have improved shear resistance and cut resistance compared tocovers made from balata or SURLYN®.

U.S. Pat. No. 5,692,974 discloses methods of using cationic ionomers ingolf ball cover compositions. Additionally, the patent relates to golfballs having covers and cores incorporating urethane ionomers. Improvedresiliency and initial velocity are achieved by the addition of analkylating agent such as t-butyl-chloride which induces ionicinteractions in the polyurethane to produce cationic type ionomers.

International Patent Application WO 98/37929 discloses a composition forgolf ball covers that comprises a blend of a diisocyanate/polyolprepolymer and a curing agent comprising a blend of a slow-reactingdiamine and a fast-reacting diamine. Improved “feel”, playability, anddurability characteristics are exhibited.

Conventional polyurethane elastomers are known to have lower resiliencythan SURLYN® and other ionomer resins. It has now been discovered thatthe use of a polyurethane composition, according to the presentinvention, in forming golf ball cores, intermediate and mantle layers,and/or covers, can raise the velocity of a golf ball prepared with thecomposition: (1) closer to the velocities observed with SURLYN®-coveredgolf balls; and (2) higher than the velocities exhibited usingalternative urethane compositions. Additionally, it is desired tocombine polyurethane cover compositions with polybutadiene corematerials, especially those having resilience indices greater than about40. Cores formed of materials such as these have been found to provideexceptional resiliency characteristics without a loss in performancecharacteristics (i.e., decreased compression).

It is thus desired to prepare golf balls having lower compression, i.e.,a softer ball, while having the same or higher resilience thanconventional balls. It is alternatively desired to obtain the same orlower compression while achieving greater resilience.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball comprising a centercomprising a polybutadiene having a molecular weight of greater than200,000 and a resilience index of at least about 40; and a cover layercomprising a polyurethane composition formed from a prepolymer having nogreater than 7.5 percent by weight unreacted isocyanate groups.Preferably, the resilience index is greater than about 50.

The prepolymer may include an isocyanate, at least one polyol, and atleast one curing agent. Preferably, the isocyanate includes4,4′-diphenylmethane diisocyanate, polymeric 4,4′-diphenylmethanediisocyanate, carbodiimide-modified liquid 4,4′-diphenylmethanediisocyanate, 4,4′-dicyclohexylmethane diisocyanate, p-phenylenediisocyanate, toluene diisocyanate, isophoronediisocyanate,p-methylxylene diisocyanate, m-methylxylene diisocyanate, o-methylxylenediisocyanate, or a mixture thereof. The at least one polyol may includepolyether polyols, hydroxy-terminated polybutadiene, polyester polyols,polycaprolactone polyols, polycarbonate polyols, and mixtures thereof.The curing agent may include a polyamine curing agent, a polyol curingagent, or a mixture thereof. It is preferred, however, that the curingagent is a polyamine curing agent.

If the polyamine is selected as the curing agent, the polyamine curingagent may include 3,5-dimethylthio-2,4-toluenediamine and isomersthereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate;N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline;phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); and mixtures thereof.

In one embodiment, however, the curing agent is a polyol curing agent.If the curing agent is a polyol, preferably, the polyol curing agentincludes ethylene glycol; diethylene glycol; polyethylene glycol;propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl) ether; trimethylol propane, andmixtures thereof.

In a another embodiment, the prepolymer has between about 2.5 percentand about 7.5 percent by weight unreacted isocyanate groups. The coverlayer preferably has a thickness of less than about 0.05 inches.Further, the center should have a Mooney viscosity of between about 40and about 80 and, preferably, between about 45 and about 60. In apreferred embodiment, the polybutadiene has a vinyl-polybutadiene isomercontent of less than about 2 percent by weight and the polybutadiene hasa cis-isomer content of at least about 95 percent by weight.

The golf ball center outer diameter is preferably of no less than about1.55 inches and, additionally, the center further includes a materialformed from a conversion reaction of polybutadiene having a first amountof trans-polybutadiene, a free radical source, and at least onecis-to-trans catalyst. Preferably, the reaction occurs at a temperaturesufficient to form a polybutadiene reaction product having an secondamount of trans-polybutadiene greater than the first amount oftrans-polybutadiene. The cis-to-trans catalyst may include at least oneof a organosulfur component, an inorganic sulfur compound, an aromaticorganometallic compound, a metal-organosulfur compound, tellurium,selenium, elemental sulfur, a polymeric sulfur, or an aromatic organiccompound. The organosulfur component may include at least one of4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamidodiphenyl disulfide. Preferably, the cis-to-trans catalyst is present inan amount from about 0.1 to 10 parts per hundred of polybutadiene.

In another embodiment, the golf ball further includes an intermediatelayer juxtaposed between the center and the cover layer, wherein theintermediate layer comprises a material formed from a conversionreaction of polybutadiene having a first amount of trans-polybutadiene,a free radical source, and a cis-to-trans catalyst comprising at leastone organosulfur component, wherein the intermediate layer has an outerdiameter of no less than about 1.58 inches, and wherein the center hasan outer diameter of less than about 1.55 inches. In yet anotherembodiment, the cover layer comprises an inner cover layer and an outercover layer, the inner cover layer juxtaposed the center and the outercover layer. Preferably, at least one of the inner and outer cover layerhas a thickness of less than about 0.05 inches.

If present, the inner cover layer is formed from at least one materialselected from the group comprising of an ionomer resin, a polyurethane,a polyetherester, a polyetheramide, a polyester, a dynamicallyvulcanized elastomer, a functionalized styrenebutadiene elastomer, ametallocene polymer, nylon, acrylonitrile butadiene-styrene copolymer orblends thereof. In still another embodiment, the inner cover has anouter diameter of at least about 1.55 inches and, preferably, betweenabout 1.58 and about 1.64 inches. In an additional embodiment, thepolyurethane is a thermoplastic or thermoset material.

The present invention is also directed to a golf ball comprising acenter comprising a polybutadiene having a molecular weight of greaterthan 300,000 and a resilience index of at least about 40; an outer corelayer having an outer diameter of no less than about 1.51 inches; aninner cover layer surrounding the outer core layer; and an outer coverlayer comprising of a polyurethane composition formed from a prepolymerhaving no greater than about 7.5 percent by weight unreacted isocyanategroups. Preferably, the resilience index is greater than about 50.

The prepolymer may include an isocyanate, at least one polyol, and atleast one curing agent. Preferably, the isocyanate includes4,4′-diphenylmethane diisocyanate, polymeric 4,4′-diphenylmethanediisocyanate, carbodiimide-modified liquid 4,4′-diphenylmethanediisocyanate, 4,4′-dicyclohexylmethane diisocyanate, p-phenylenediisocyanate, toluene diisocyanate, isophoronediisocyanate,p-methylxylene diisocyanate, m-methylxylene diisocyanate, o-methylxylenediisocyanate, or a mixture thereof. The at least one polyol may includepolyether polyols, hydroxy-terminated polybutadiene, polyester polyols,polycaprolactone polyols, polycarbonate polyols, and mixtures thereof.The curing agent may include a polyamine curing agent, a polyol curingagent, or a mixture thereof. It is preferred, however, that the curingagent is a polyamine curing agent.

If the polyamine is selected as the curing agent, the polyamine curingagent may include 3,5-dimethylthio-2,4-toluenediamine and isomersthereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate;N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline;phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); and mixtures thereof.

In one embodiment, however, the curing agent is a polyol curing agent.If the curing agent is a polyol, preferably, the polyol curing agentincludes ethylene glycol; diethylene glycol; polyethylene glycol;propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene;1,4-butanediol;1,5-pentanediol; 1,6-hexanediol;resorcinol-di-(-hydroxyethyl)ether;hydroquinone-di-(-hydroxyethyl)ether; trimethylol propane, and mixturesthereof.

In a another embodiment, the prepolymer has between about 2.5 percentand about 7.5 percent by weight unreacted isocyanate groups. At leastone of the inner and outer cover layers preferably has a thickness ofless than about 0.05 inches. Further, the center should have a Mooneyviscosity of between about 40 and about 80. In a preferred embodiment,the polybutadiene has a vinyl-polybutadiene isomer content of less thanabout 2 percent by weight and the polybutadiene has a cis-isomer contentof at least about 95 percent by weight.

The golf ball center outer diameter is preferably of no less than about1.55 inches and, additionally, the center further includes a materialformed from a conversion reaction of polybutadiene having a first amountof trans-polybutadiene, a free radical source, and at least onecis-to-trans catalyst. Preferably, the reaction occurs at a temperaturesufficient to form a polybutadiene reaction product having an secondamount of trans-polybutadiene greater than the first amount oftrans-polybutadiene. The cis-to-trans catalyst may include at least oneof an organosulfur compound, an inorganic sulfur compound, an aromaticorganometallic compound, a metal-organosulfur compound, tellurium,selenium, elemental sulfur, a polymeric sulfur, or an aromatic organiccompound. The organosulfur component may include at least one of4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamidodiphenyl disulfide. Preferably, the cis-to-trans catalyst is present inan amount from about 0.1 to 10 parts per hundred of polybutadiene.

In one embodiment, the inner cover layer includes an ionomer resin, apolyurethane, a polyetherester, a polyetheramide, a polyester, adynamically vulcanized elastomer, a functionalized styrenebutadieneelastomer, a metallocene polymer nylon, acrylonitrile butadiene-styrenecopolymer or blends thereof. The inner cover may have an outer diameterof at least about 1.55 inches and, preferably, between about 1.58 andabout 1.64 inches. In an additional embodiment, the polyurethane is athermoplastic or thermoset material.

The present invention is also directed to a golf ball comprising acenter formed of a cis-polybutadiene having a molecular weight ofgreater than 300,000 and a resilience index of at least about 40; anouter core layer having an outer diameter of no less than about 1.51inches; an inner cover layer surrounding the outer core layer, the innercover layer comprising a polyurethane; and an outer cover layercomprising an ionomer or an elastomeric material.

The present invention is also directed to a golf ball comprising acenter comprising a polybutadiene having a molecular weight of greaterthan 300,000 and a resilience index of at least about 40; an outer corelayer having an outer diameter of no less than about 1.51 inches; aninner cover layer surrounding the outer core layer; and an outer coverlayer; wherein the inner and outer cover layers are formed of apolyurethane composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a two-piece golf ball having a coverand a core according to the invention;

FIG. 2 is a cross-section of a golf ball having an intermediate layerbetween a cover and a center according to the invention; and

FIG. 3 is a cross-section of a golf ball having more than oneintermediate layer between a cover and a center according to theinvention.

DEFINITIONS

The term “about,” as used herein in connection with one or more numbersor numerical ranges, should be understood to refer to all such numbers,including all numbers in a range.

As used herein, “cis-to-trans catalyst” means any component or acombination thereof that will convert at least a portion ofcis-polybutadiene isomer to trans-polybutadiene isomer at a giventemperature. It should be understood that the combination of thecis-isomer, the trans-isomer, and any vinyl-isomer, measured at anygiven time, comprises 100 percent of the polybutadiene.

As used herein, the term “active ingredients” is defined as the specificcomponents of a mixture or blend that are essential to the chemicalreaction.

As used herein, substituted and unsubstituted “aryl” groups means ahydrocarbon ring bearing a system of conjugated double bonds, typicallycomprising 4n+2π ring electrons, where n is an integer. Examples of arylgroups include, but are not limited to phenyl, naphthyl, anisyl, tolyl,xylenyl and the like. According to the present invention, aryl alsoincludes heteroaryl groups, e.g., pyrimidine or thiophene. These arylgroups may also be substituted with any number of a variety offunctional groups. In addition to the functional groups described hereinin connection with carbocyclic groups, functional groups on the arylgroups can include hydroxy and metal salts thereof; mercapto and metalsalts thereof; halogen; amino, nitro, cyano, and amido; carboxylincluding esters, acids, and metal salts thereof; silyl; acrylates andmetal salts thereof; sulfonyl or sulfonamide; and phosphates andphosphites; and a combination thereof.

As used herein, the term “Atti compression” is defined as the deflectionof an object or material relative to the deflection of a calibratedspring, as measured with an Atti Compression Gauge, that is commerciallyavailable from Atti Engineering Corp. of Union City, N.J. Atticompression is typically used to measure the compression of a golf ball.When the Atti Gauge is used to measure cores having a diameter of lessthan 1.680 inches, it should be understood that a metallic or othersuitable shim is used to make the measured object 1.680 inches indiameter. However, when referring to the compression of a core, it ispreferred to use a compressive load measurement. The term “compressiveload” is defined as the normalized load in pounds for a 10.8-percentdiametrical deflection for a spherical object having a diameter of 1.58inches.

As used herein, substituted and unsubstituted “carbocyclic” means cycliccarbon-containing compounds, including, but not limited to cyclopentyl,cyclohexyl, cycloheptyl, adamantyl, and the like. Such cyclic groups mayalso contain various substituents in which one or more hydrogen atomshas been replaced by a functional group. Such functional groups includethose described above, and lower alkyl groups having from 1-28 carbonatoms. The cyclic groups of the invention may further comprise aheteroatom.

As used herein, the term “coefficient of restitution” for golf balls isdefined as the ratio of the rebound velocity to the inbound velocitywhen balls are fired into a rigid plate. The inbound velocity isunderstood to be 125 ft/s.

As used herein, the term “dynamic stiffness” is defined as load dividedby the deflection for a 1.4-mm spherical radius penetration probeoscillating at 1 Hz with an amplitude of 100 μm. The probe dynamicallypenetrates the surface of a sample material. Material samples ofspherical cores were prepared by sectioning out a 6-mm-thick layer alongthe equator of core to produce a disk 6 mm thick with one surfacecontaining the geometric center of the core. By positioning the probe atany selected radial position on the disk, a dynamic stiffnessmeasurement may be obtained. Accurate dynamic measurements may be madeby keeping the material sample at a substantially uniform temperature.The dynamic stiffness was acquired using a Dynamic Mechanical Analyzer,Model DMA 2980 available from TA Instruments Corporation of New Castle,Del. The instrument setting for the DMA 2980 were 1-Hz frequency, 100-μmamplitude, 0.3-N static load, and auto strain of 105 percent. The 1.4-mmspherical radius probe is available from TA Instruments as a penetrationkit accessory to the DMA 2980. The DMA 2980 is equipped with atemperature-controlled chamber that enables testing at a wide variety ofambient temperatures.

The method and instrument utilized for measuring “dynamic stiffness” mayalso be used to measure loss tangent (also commonly referred to as tanδ). Loss tangent is the ratio of loss modulus to storage modulus. Lossmodulus is the portion of modulus which is out of phase withdisplacement and storage modulus is the portion of modulus which is inphase with displacement. The DMA 2980 automatically calculates andreports loss tangent.

As used herein, the terms “Group VIA component” or “Group VIA element”mean a component that includes a sulfur component, a selenium component,or a tellurium component, or a combination thereof.

As used herein, the term “sulfur component” means a component that iselemental sulfur, polymeric sulfur, or a combination thereof. It shouldbe further understood that “elemental sulfur” refers to the ringstructure of S₈ and that “polymeric sulfur” is a structure including atleast one additional sulfur relative to the elemental sulfur.

As used herein, the term “fluid” includes a liquid, a paste, a gel, agas, or any combination thereof.

As used herein, the term “molecular weight” is defined as the absoluteweight average molecular weight. The molecular weight is determined bythe following method: approximately 20 mg of polymer is dissolved in 10mL of tetrahydrofuran (“THF”), which may take a few days at roomtemperature depending on the polymer's molecular weight anddistribution. One liter of THF is filtered and degassed before beingplaced in a high-performance liquid chromatography (“HPLC”) reservoir.The flow rate of the HPLC is set to 1 mL/min through a Viscogel column.This non-shedding, mixed bed, column model GMH_(HR)-H, which has an IDof 7.8 mm and 300 mm long is available from Viscotek Corp. of Houston,Tex. The THF flow rate is set to 1 mL/min for at least one hour beforesample analysis is begun or until stable detector baselines areachieved. During this purging of the column and detector, the internaltemperature of the Viscotek TDA Model 300 triple detector should be setto 40° C. This detector is also available from Viscotek Corp. The threedetectors (i.e., Refractive Index, Differential Pressure, and LightScattering) and the column should be brought to thermal equilibrium, andthe detectors should be purged and zeroed, to prepare the system forcalibration according to the instructions provided with this equipment.A 100-μL aliquot of sample solution can then be injected into theequipment and the molecular weight of each sample can be calculated withthe Viscotek's triple detector software. When the molecular weight ofthe polybutadiene material is measured, a dn/dc of 0.130 should alwaysbe used. It should be understood that this equipment and these methodsprovide the molecular weight numbers described and claimed herein, andthat other equipment or methods will not necessarily provide equivalentvalues as used herein.

As used herein, the term “multilayer” means at least two layers andincludes liquid center balls, wound balls, hollow-center balls, andballs with at least two intermediate layers and/or an inner or outercover.

As used herein, the term “parts per hundred,” also known as “phr,” isdefined as the number of parts by weight of a particular componentpresent in a mixture, relative to 100 parts by weight of the totalpolymer component. Mathematically, this can be expressed as the weightof an ingredient divided by the total weight of the polymer, multipliedby a factor of 100.

As used herein, the term “substantially free” means less than about 5weight percent, preferably less than about 3 weight percent, morepreferably less than about 1 weight percent, and most preferably lessthan about 0.01 weight percent.

As used herein the term “resilience index” is defined as the differencein loss tangent measured at 10 cpm and 1000 cpm divided by 990 (thefrequency span) multiplied by 100,000 (for normalization and unitconvenience). The loss tangent is measured using an RPA 2000manufactured by Alpha Technologies of Akron, Ohio. The RPA 2000 is setto sweep from 2.5 to 1000 cpm at a temperature of 100° C. using an arcof 0.5 degrees. An average of six loss tangent measurements wereacquired at each frequency and the average is used in calculation of theresilience index. The computation of resilience index is as follows:Resilience Index=100,000·[(loss tangent @10 cpm)−(loss tangent @1000cpm)]/990

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a golf ball 10 of the present invention can includea core 12, a cover 16, and optional inner cover layer 16 a surroundingthe core 12. Referring to FIG. 2, a golf ball 20 of the presentinvention can include a center 22, a cover 26, an inner cover layer 26a, and at least one intermediate layer 24 disposed between the cover andthe center. Each of the cover and center may also include more than onelayer; i.e., the golf ball can be a conventional three-piece wound ball,a two-piece ball, a ball having a multi-layer core or an intermediatelayer or layers, etc. Thus, referring to FIG. 3, a golf ball 30 of thepresent invention can include a center 32, a cover 38, and intermediatelayers 34 and 36 disposed between the cover and the center. AlthoughFIG. 3 shows only two intermediate layers, it will be appreciated thatany number or type of intermediate layers may be used, as desired. Thepresent invention relates to two piece golf balls having a core and acover, or multilayer golf balls having a solid, hollow, or fluid-filledcenter, a cover, and at least one intermediate layer disposedconcentrically adjacent to the center. At least one of the center oroptional intermediate layer includes a reaction product that includes acis-to-trans catalyst, a resilient polymer component havingpolybutadiene, a free radical source, and optionally, a crosslinkingagent, a filler, or both. Preferably, the reaction product has a firstdynamic stiffness measured at −50° C. that is less than about 130percent of a second dynamic stiffness measured at 0° C. More preferably,the first dynamic stiffness is less than about 125 percent of the seconddynamic stiffness. Most preferably, the first dynamic stiffness is lessthan about 110 percent of the second dynamic stiffness.

The invention also includes a method to convert the cis-isomer of thepolybutadiene resilient polymer component to the trans-isomer during amolding cycle and to form a golf ball. Various combinations of polymers,cis-to-trans catalysts, fillers, crosslinkers, and a source of freeradicals, may be used. To obtain a higher resilience and lowercompression center or intermediate layer, a high-molecular weightpolybutadiene with a cis-isomer content preferably greater than about 90percent is converted to increase the percentage of trans-isomer contentat any point in the golf ball or portion thereof, preferably to increasethe percentage throughout substantially all of the golf ball or portionthereof, during the molding cycle. More preferably, thecis-polybutadiene isomer is present in an amount of greater than about95 percent of the total polybutadiene content. Without wishing to bebound by any particular theory, it is believed that a low amount of1,2-polybutadiene isomer(“vinyl-polybutadiene”) is desired in theinitial polybutadiene, and the reaction product. Typically, the vinylpolybutadiene isomer content is less than about 7 percent. Preferably,the vinyl polybutadiene isomer content is less than about 4 percent.More preferably, the vinyl polybutadiene isomer content is less thanabout 2 percent. Without wishing to be bound by any particular theory,it is also believed that the resulting mobility of the combined cis- andtrans-polybutadiene backbone is responsible for the lower modulus andhigher resilience of the reaction product and golf balls including thesame.

To produce a polymer reaction product that exhibits the higherresilience and lower modulus (low compression) properties that aredesirable and beneficial to golf ball playing characteristics,high-molecular-weight cis-1,4-polybutadiene, preferably may be convertedto the trans-isomer during the molding cycle. The polybutadiene materialtypically has a molecular weight of greater than about 200,000.Preferably, the polybutadiene molecular weight is greater than about250,000, more preferably between about 300,000 and 500,000. Withoutwishing to be bound by any particular theory, it is believed that thecis-to-trans catalyst component, in conjunction with the free radicalsource, acts to convert a percentage of the polybutadiene polymercomponent from the cis-to the trans-conformation. The cis-to-transconversion requires the presence of a cis-to-trans catalyst, such as anorganosulfur or metal-containing organosulfur compound, a substituted orunsubstituted aromatic organic compound that does not contain sulfur ormetal, an inorganic sulfide compound, an aromatic organometalliccompound, or mixtures thereof. The cis-to-trans catalyst component mayinclude one or more of the other cis-to-trans catalysts describedherein.

In one embodiment, the at least one organosulfur component issubstantially free of metal, which typically means less than about 10weight percent metal, preferably less than about 3 weight percent metal,more preferably less than about 1 weight percent metal, and mostpreferably only trace amounts of metal, such as less than about 0.01weight percent.

As used herein when referring to the invention, the term “organosulfurcompound(s)” or “organosulfur component(s),” means at least one of4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyldisulfide; bis(2-aminophenyl)disulfide; bis(4-aminophenyl)disulfide;bis(3-aminophenyl)disulfide; 2,2′-bis(4-aminonaphthyl)disulfide;2,2′-bis(3-aminonaphthyl)disulfide; 2,2′-bis(4-aminonaphthyl)disulfide;2,2′-bis(5-aminonaphthyl)disulfide; 2,2′-bis(6-aminonaphthyl)disulfide;2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl)disulfide;1,1′-bis(2-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl)disulfide;1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(4-aminonaphthyl)disulfide;1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl)disulfide;1,1′-bis(7-aminonaphthyl)disulfide; 1,1′-bis(8-aminonaphthyl)disulfide;1,2′-diamino-1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl)disulfide;bis(2-chlorophenyl)disulfide; bis(3-chlorophenyl)disulfide;bis(4-bromophenyl)disulfide; bis(2-bromophenyl)disulfide;bis(3-bromophenyl)disulfide; bis(4-fluorophenyl)disulfide;bis(4-iodophenyl)disulfide; bis(2,5-dichlorophenyl)disulfide;bis(3,5-dichlorophenyl)disulfide; bis(2,4-dichlorophenyl)disulfide;bis(2,6-dichlorophenyl)disulfide; bis(2,5-dibromophenyl)disulfide;bis(3,5-dibromophenyl)disulfide; bis(2-chloro-5-bromophenyl)disulfide;bis(2,4,6-trichlorophenyl)disulfide;bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl)disulfide;bis(2-cyanophenyl)disulfide; bis(4-nitrophenyl)disulfide;bis(2-nitrophenyl)disulfide; 2,2′-dithiobenzoic acid ethylester;2,2′-dithiobenzoic acid methylester; 2,2′-dithiobenzoic acid;4,4′-dithiobenzoic acid ethylester; bis(4-acetylphenyl)disulfide;bis(2-acetylphenyl)disulfide; bis(4-formylphenyl)disulfide;bis(4-carbamoylphenyl)disulfide; 1,1′-dinaphthyl disulfide;2,2′-dinaphthyl disulfide; 1,2′-dinaphthyl disulfide;2,2′-bis(1-chlorodinaphthyl)disulfide;2,2′-bis(1-bromonaphthyl)disulfide; 1,1′-bis(2-chloronaphthyl)disulfide;2,2′-bis(1-cyanonaphtyl)disulfide; 2,2′-bis(1-acetylnaphthyl)disulfide;and the like; or a mixture thereof. Preferred organosulfur componentsinclude 4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or2,2′-benzamido diphenyl disulfide, or a mixture thereof. A morepreferred organosulfur component includes 4,4′-ditolyl disulfide. Theorganosulfur cis-to-trans catalyst, when present, is preferably presentin an amount sufficient to produce the reaction product so as to containat least about 12 percent trans-polybutadiene isomer, but typically isgreater than about 32 percent trans-polybutadiene isomer based on thetotal resilient polymer component. Suitable metal-containingorganosulfur components include, but are not limited to, cadmium,copper, lead, and tellurium analogs of diethyldithiocarbamate,diamyldithiocarbamate, and dimethyldithiocarbamate, or mixtures thereof.Suitable substituted or unsubstituted aromatic organic components thatdo not include sulfur or a metal include, but are not limited to,4,4′-diphenyl acetylene, azobenzene, or a mixture thereof. The aromaticorganic group preferably ranges in size from C₆ to C₂₀, and morepreferably from C₆ to C₁₀. Suitable inorganic sulfide componentsinclude, but are not limited to titanium sulfide, manganese sulfide, andsulfide analogs of iron, calcium, cobalt, molybdenum, tungsten, copper,selenium, yttrium, zinc, tin, and bismuth. The cis-to-trans catalyst mayalso be a blend of an organosulfur component and an inorganic sulfidecomponent.

A substituted or unsubstituted aromatic organic compound may also beincluded in the cis-to-trans catalyst. In one embodiment, the aromaticorganic compound is substantially free of metal. Suitable substituted orunsubstituted aromatic organic components include, but are not limitedto, components having the formula (R₁)_(x)—R₃-M-R₄—(R₂)_(y), wherein R₁and R₂ are each hydrogen or a substituted or unsubstituted C₁₋₂₀ linear,branched, or cyclic alkyl, alkoxy, or alkylthio group, or a single,multiple, or fused ring C₆ to C₂₄ aromatic group; x and y are each aninteger from 0 to 5; R₃ and R₄ are each selected from a single,multiple, or fused ring C₆ to C₂₄ aromatic group; and M includes an azogroup or a metal component. R₃ and R₄ are each preferably selected froma C₆ to C₁₀ aromatic group, more preferably selected from phenyl,benzyl, naphthyl, benzamido, and benzothiazyl. R₁ and R₂ are eachpreferably selected from a substituted or unsubstituted C₁₋₁₀ linear,branched, or cyclic alkyl, alkoxy, or alkylthio group or a C₆ to C₁₀aromatic group. When R₁, R₂, R₃, or R₄, are substituted, thesubstitution may include one or more of the following substituentgroups: hydroxy and metal salts thereof; mercapto and metal saltsthereof; halogen; amino, nitro, cyano, and amido; carboxyl includingesters, acids, and metal salts thereof; silyl; acrylates and metal saltsthereof; sulfonyl or sulfonamide; and phosphates and phosphites. When Mis a metal component, it may be any suitable elemental metal availableto those of ordinary skill in the art. Typically, the metal will be atransition metal, although preferably it is tellurium or selenium.

The cis-to-trans catalyst can also include a Group VIA component, asdefined herein. Elemental sulfur and polymeric sulfur are commerciallyavailable from, e.g., Elastochem, Inc. of Chardon, Ohio. Exemplarysulfur catalyst compounds include PB(RM-S)-80 elemental sulfur andPB(CRST)-65 polymeric sulfur, each of which is available fromElastochem, Inc. An exemplary tellurium catalyst under the tradenameTELLOY and an exemplary selenium catalyst under the tradename VANDEX areeach commercially available from RT Vanderbilt.

The cis-to-trans catalyst is preferably present in an amount from about0.1 to 10 parts per hundred of the total resilient polymer component.More preferably, the cis-to-trans catalyst is present in an amount fromabout 0.1 to 5 parts per hundred of the total resilient polymercomponent. Most preferably, the cis-to-trans catalyst is present in anamount from about 0.1 to 8 parts per hundred of the total resilientpolymer component. The cis-to-trans catalyst is typically present in anamount sufficient to produce the reaction product so as to increase thetrans-polybutadiene isomer content to contain from about 5 percent to 70percent trans-polybutadiene based on the total resilient polymercomponent.

The measurement of trans-isomer content of polybutadiene referred toherein was and can be accomplished as follows. Calibration standards areprepared using at least two polybutadiene rubber samples of knowntrans-content, e.g., high and low percent trans-polybutadiene). Thesesamples are used alone and blended together in such a way as to create aladder of trans-polybutadiene content of at least about 1.5% to 50% orto bracket the unknown amount, such that the resulting calibration curvecontains at least about 13 equally spaced points.

Using a commercially available Fourier Transform Infrared (“FTIR”)spectrometer equipped with a Photoacoustic (“PAS”) cell, a PAS spectrumof each standard was obtained using the following instrument parameters:scan at speed of 2.5 KHz (0.16 cm/s optical velocity), use a 1.2 KHzelectronic filter, set an undersampling ratio of 2 (number of lasersignal zero crossings before collecting a sample), co-add a minimum of128 scans at a resolution of 4 cm⁻¹ over a range of 375 to 4000 cm⁻¹with a sensitivity setting of 1.

The cis-, trans-, and vinyl-polybutadiene peaks are typically foundbetween 600 and 1100 cm⁻¹ in the PAS spectrum. The area under each ofthe trans-polybutadiene peaks can be integrated. Determining thefraction of each peak area relative to the total area of the threeisomer peaks allow construction of a calibration curve of thetrans-polybutadiene area fraction versus the actual trans-polybutadienecontent. The correlation coefficient (R²) of the resulting calibrationcurve must be a minimum of 0.95.

A PAS spectrum is obtained, using the parameters described above, forthe unknown core material at the point of interest (e.g., the surface orcenter of the core) by filling the PAS cell with a sample containing afreshly cut, uncontaminated surface free of foreign matters, such asmold release and the like. The trans-polybutadiene area fraction of theunknown is analyzed to determine the actual trans-isomer content fromthe calibration curve.

In one known circumstance when barium sulfate is included, the abovemethod for testing trans-content may be less accurate. Thus, anadditional or alternative test of the trans-content of polybutadiene isas follows. Calibration standards are prepared using at least twopolybutadienes of known trans-content (e.g., high and low percenttrans-polybutadiene). These samples are used alone and blended togetherin such a way as to create a ladder of trans-polybutadiene content of atleast about 1.5% to 50% or to bracket the unknown amount, such that theresulting calibration curve contains at least about 13 equally spacedpoints.

Using a Fourier Transform Raman (“FT-Raman”) spectrometer equipped witha near-infrared laser, a Stokes Raman spectrum should be obtained fromeach standard using the following instrument parameters: sufficientlaser power to obtain a good signal-to-noise ratio (“S/N”) withoutcausing excessive heating or fluorescence (typically about 400 to 800 mWis suitable); a resolution of 2 cm⁻¹; over a Raman shift spectral rangeof about 400 to 4000 cm⁻¹; and co-adding at least 300 scans.

A calibration curve may be constructed from the data generated above,using a chemometrics approach and software such as PLSplus/IQ fromGalactic Industries Corp. of Salem, N.H. An acceptable calibration wasobtained with this software using a PLS-1 curve generated using an SNV(detrend) pathlength correction, a mean center data preparation, and a5-point SG second derivative over the spectral range from about 1600 to1700 cm⁻¹. The correlation coefficient (R²) of the resulting calibrationcurve must be a minimum of 0.95.

A Raman spectrum of the core material is obtained using this instrumentat the point of interest in the sample (e.g., surface or center of thegolf ball core). The sample must be free of foreign matter, such as moldrelease, etc. Analyze the spectrum of the sample using the PLScalibration curve to determine trans-polybutadiene isomer content of thesample.

A free-radical source, often alternatively referred to as a free-radicalinitiator, is required in the composition and method. The free-radicalsource is typically a peroxide, and preferably an organic peroxide.Suitable free-radical sources include di-t-amyl peroxide,di(2-t-butyl-peroxyisopropyl)benzene peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-t-butyl peroxide, 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxy)valerate, lauryl peroxide, benzoylperoxide, t-butyl hydroperoxide, and the like, and any mixture thereof.The peroxide is typically present in an amount greater than about 0.1parts per hundred of the total resilient polymer component, preferablyabout 0.1 to 15 parts per hundred of the resilient polymer component,and more preferably about 0.2 to 5 parts per hundred of the totalresilient polymer component. It should be understood by those ofordinary skill in the art that the presence of certain cis-to-transcatalysts according to the invention may require a larger amount offree-radical source, such as the amounts described herein, compared toconventional cross-linking reactions. The free radical source mayalternatively or additionally be one or more of an electron beam, UV orgamma radiation, x-rays, or any other high energy radiation sourcecapable of generating free radicals. It should be further understoodthat heat often facilitates initiation of the generation of freeradicals.

Crosslinkers are included to increase the hardness of the reactionproduct. Suitable crosslinking agents include one or more metallic saltsof unsaturated fatty acids or monocarboxylic acids, such as zinc,calcium, or magnesium acrylate salts, and the like, and mixturesthereof. Preferred acrylates include zinc acrylate, zinc diacrylate,zinc methacrylate, and zinc dimethacrylate, and mixtures thereof. Thecrosslinking agent must be present in an amount sufficient to crosslinka portion of the chains of polymers in the resilient polymer component.For example, the desired compression may be obtained by adjusting theamount of crosslinking. This may be achieved, for example, by alteringthe type and amount of crosslinking agent, a method well-known to thoseof ordinary skill in the art. The crosslinking agent is typicallypresent in an amount greater than about 0.1 percent of the resilientpolymer component, preferably from about 10 to 40 percent of theresilient polymer component, more preferably from about 10 to 30 percentof the resilient polymer component. When an organosulfur is selected asthe cis-to-trans catalyst, zinc diacrylate may be selected as thecrosslinking agent and is present in an amount of less than about 25phr.

Fillers added to one or more portions of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, the specific gravity (i.e., density-modifying fillers), themodulus, the tear strength, reinforcement, and the like. The fillers aregenerally inorganic, and suitable fillers include numerous metals ormetal oxides, such as zinc oxide and tin oxide, as well as bariumsulfate, zinc sulfate, calcium carbonate, barium carbonate, clay,tungsten, tungsten carbide, an array of silicas, and mixtures thereof.Fillers may also include various foaming agents or blowing agents whichmay be readily selected by one of ordinary skill in the art. Polymeric,ceramic, metal, and glass microspheres may be solid or hollow, andfilled or unfilled. Fillers are typically also added to one or moreportions of the golf ball to modify the density thereof to conform touniform golf ball standards. Fillers may also be used to modify theweight of the center or at least one additional layer for specialtyballs, e.g., a lower weight ball is preferred for a player having a lowswing speed.

The polymers, free-radical initiator, filler(s), and any other materialsused in forming either the golf ball center or any portion of the core,in accordance with invention, may be combined to form a mixture by anytype of mixing known to one of ordinary skill in the art. Suitable typesof mixing include single pass and multi-pass mixing, and the like. Thecrosslinking agent, and any other optional additives used to modify thecharacteristics of the golf ball center or additional layer(s), maysimilarly be combined by any type of mixing. A single-pass mixingprocess where ingredients are added sequentially is preferred, as thistype of mixing tends to increase efficiency and reduce costs for theprocess. The preferred mixing cycle is single step wherein the polymer,cis-trans catalyst, filler, zinc diacrylate, and peroxide are addedsequentially. Suitable mixing equipment is well known to those ofordinary skill in the art, and such equipment may include a Banburymixer, a two-roll mill, or a twin screw extruder. Conventional mixingspeeds for combining polymers are typically used, although the speedmust be high enough to impart substantially uniform dispersion of theconstituents. On the other hand, the speed should not be too high, ashigh mixing speeds tend to break down the polymers being mixed andparticularly may undesirably decrease the molecular weight of theresilient polymer component. The speed should thus be low enough toavoid high shear, which may result in loss of desirably high molecularweight portions of the polymer component. Also, too high a mixing speedmay undesirably result in creation of enough heat to initiate thecrosslinking before the preforms are shaped and assembled around a core.The mixing temperature depends upon the type of polymer components, andmore importantly, on the type of free-radical initiator. For example,when using di(2-t-butyl-peroxyisopropyl)benzene as the free-radicalinitiator, a mixing temperature of about 80° C. to 125° C., preferablyabout 88° C. to 110° C., and more preferably about 90° C. to 100° C. issuitable to safely mix the ingredients. Additionally, it is important tomaintain a mixing temperature below the peroxide decompositiontemperature. For example, if dicumyl peroxide is selected as theperoxide, the temperature should not exceed 200° F. Suitable mixingspeeds and temperatures are well-known to those of ordinary skill in theart, or may be readily determined without undue experimentation.

The mixture can be subjected to, e.g., a compression or injectionmolding process, to obtain solid spheres for the center or hemisphericalshells for forming an intermediate layer. The polymer mixture issubjected to a molding cycle in which heat and pressure are appliedwhile the mixture is confined within a mold. The cavity shape depends onthe portion of the golf ball being formed. The compression and heatliberates free radicals by decomposing one or more peroxides, which mayinitiate the cis-to-trans conversion and crosslinking simultaneously.The temperature and duration of the molding cycle are selected basedupon the type of peroxide and cis-trans catalyst selected. The moldingcycle may have a single step of molding the mixture at a singletemperature for a fixed time duration. An example of a single stepmolding cycle, for a mixture that contains dicumyl peroxide, would holdthe polymer mixture at 340° F. for a duration of 15 minutes. The moldingcycle may also include a two-step process, in which the polymer mixtureis held in the mold at an initial temperature for an initial duration oftime, followed by holding at a second, typically higher temperature fora second duration of time. An example of a two-step molding cycle wouldbe holding the mold at 290° F. for 40 minutes, then ramping the mold to340° F. where it is held for a duration of 20 minutes. In a preferredembodiment of the current invention, a single-step cure cycle isemployed. Single-step processes are effective and efficient, reducingthe time and cost of a two-step process. The resilient polymercomponent, polybutadiene, cis-to-trans conversion catalyst, additionalpolymers, free-radical initiator, filler, and any other materials usedin forming either the golf ball center or any portion of the core, inaccordance with the invention, may be combined to form a golf ball by aninjection molding process, which is also well-known to one of ordinaryskill in the art. Although the curing time depends on the variousmaterials selected, a particularly suitable curing time is about 5 to 18minutes, preferably from about 8 to 15 minutes, and more preferably fromabout 10 to 12 minutes. Those of ordinary skill in the art will bereadily able to adjust the curing time upward or downward based on theparticular materials used and the discussion herein.

The cured resilient polymer component, which contains a greater amountof trans-polybutadiene than the uncured resilient polymer component, isformed into an article having a first hardness at a point in theinterior and a surface having a second hardness such that the secondhardness differs from the first hardness by greater than 10 percent ofthe first hardness. Preferably, the article is a sphere and the point isthe midpoint of the article. In another embodiment, the second hardnessdiffers from the first by greater than 20 percent of the first hardness.The cured article also has a first amount of trans-polybutadiene at aninterior location and a second amount of trans-polybutadiene at asurface location, wherein the first amount is at least about 6 percentless than the second amount, preferably at least about 10 percent lessthan the second amount, and more preferably at least about 20 percentless than the second amount. The interior location is preferably amidpoint and the article is preferably a sphere. The compression of thecore, or portion of the core, of golf balls prepared according to theinvention is preferably below about 50, more preferably below about 25.

The cover provides the interface between the ball and a club. Propertiesthat are desirable for the cover are good moldability, high abrasionresistance, high tear strength, high resilience, and good mold release,among others. The cover typically has a thickness to provide sufficientstrength, good performance characteristics and durability. The coverpreferably has a thickness of less than about 0.1 inches, morepreferably, less than about 0.05 inches, and most preferably, betweenabout 0.02 and about 0.04 inches. The invention is particularly directedtowards a multilayer golf ball which comprises a core, an inner coverlayer, and an outer cover layer. In this embodiment, preferably, atleast one of the inner and outer cover layers has a thickness of lessthan about 0.05 inches, more preferably between about 0.02 and about0.04 inches. Most preferably, the thickness of either layer is about0.03 inches.

When the golf ball of the present invention includes an intermediatelayer, such as an inner cover layer, this layer can include anymaterials known to those of ordinary skill in the art, includingthermoplastic and thermosetting materials, but preferably theintermediate layer can include any suitable materials, such as ioniccopolymers of ethylene and an unsaturated monocarboxylic acid which areavailable under the trademark SURLYN of E.I. DuPont de Nemours & Co., ofWilmington, Del., or IOTEK or ESCOR of Exxon. These are copolymers orterpolymers of ethylene and methacrylic acid or acrylic acid partiallyneutralized with salts of zinc, sodium, lithium, magnesium, potassium,calcium, manganese, nickel or the like, in which the salts are thereaction product of an olefin having from 2 to 8 carbon atoms and anunsaturated monocarboxylic acid having 3 to 8 carbon atoms. Thecarboxylic acid groups of the copolymer may be totally or partiallyneutralized and might include methacrylic, crotonic, maleic, fumaric oritaconic acid.

This golf ball can likewise include one or more homopolymeric orcopolymeric intermediate materials, such as:

-   -   (1) Vinyl resins, such as those formed by the polymerization of        vinyl chloride, or by the copolymerization of vinyl chloride        with vinyl acetate, acrylic esters or vinylidene chloride;    -   (2) Polyolefins, such as polyethylene, polypropylene,        polybutylene and copolymers such as ethylene methylacrylate,        ethylene ethylacrylate, ethylene vinyl acetate, ethylene        methacrylic or ethylene acrylic acid or propylene acrylic acid        and copolymers and homopolymers produced using a single-site        catalyst or a metallocene catalyst;    -   (3) Polyurethanes, such as those prepared from polyols and        diisocyanates or polyisocyanates and those disclosed in U.S.        Pat. No. 5,334,673;    -   (4) Polyureas, such as those disclosed in U.S. Pat. No.        5,484,870;    -   (5) Polyamides, such as poly(hexamethylene adipamide) and others        prepared from diamines and dibasic acids, as well as those from        amino acids such as poly(caprolactam), and blends of polyamides        with SURLYN, polyethylene, ethylene copolymers,        ethyl-propylene-non-conjugated diene terpolymer, and the like;    -   (6) Acrylic resins and blends of these resins with poly vinyl        chloride, elastomers, and the like;    -   (7) Thermoplastics, such as urethanes; olefinic thermoplastic        rubbers, such as blends of polyolefins with        ethylene-propylene-non-conjugated diene terpolymer; block        copolymers of styrene and butadiene, isoprene or        ethylene-butylene rubber; or copoly(ether-amide), such as PEBAX,        sold by ELF Atochem of Philadelphia, Pa.;    -   (8) Polyphenylene oxide resins or blends of polyphenylene oxide        with high impact polystyrene as sold under the trademark NORYL        by General Electric Company of Pittsfield, Mass.;    -   (9) Thermoplastic polyesters, such as polyethylene        terephthalate, polybutylene terephthalate, polyethylene        terephthalate/glycol modified and elastomers sold under the        trademarks HYTREL by E.I. DuPont de Nemours & Co. of Wilmington,        Del., and LOMOD by General Electric Company of Pittsfield,        Mass.;    -   (10) Blends and alloys, including polycarbonate with        acrylonitrile butadiene styrene, polybutylene terephthalate,        polyethylene terephthalate, styrene maleic anhydride,        polyethylene, elastomers, and the like, and polyvinyl chloride        with acrylonitrile butadiene styrene or ethylene vinyl acetate        or other elastomers; and    -   (11) Blends of thermoplastic rubbers with polyethylene,        propylene, polyacetal, nylon, polyesters, cellulose esters, and        the like.

Preferably, the optional intermediate layer includes polymers, such asethylene, propylene, butene-1 or hexane-1 based homopolymers orcopolymers including functional monomers, such as acrylic andmethacrylic acid and fully or partially neutralized ionomer resins andtheir blends, methyl acrylate, methyl methacrylate homopolymers andcopolymers, imidized, amino group containing polymers, polycarbonate,reinforced polyamides, polyphenylene oxide, high impact polystyrene,polyether ketone, polysulfone, poly(phenylene sulfide),acrylonitrile-butadiene, acrylic-styrene-acrylonitrile, poly(ethyleneterephthalate), poly(butylene terephthalate), poly(ethelyne vinylalcohol), poly(tetrafluoroethylene) and their copolymers includingfunctional comonomers, and blends thereof. Suitable cover compositionsalso include a polyether or polyester thermoplastic urethane, athermoset polyurethane, a low modulus ionomer, such as acid-containingethylene copolymer ionomers, including E/X/Y terpolymers where E isethylene, X is an acrylate or methacrylate-based softening comonomerpresent in about 0 to 50 weight percent and Y is acrylic or methacrylicacid present in about 5 to 35 weight percent. More preferably, in a lowspin rate embodiment designed for maximum distance, the acrylic ormethacrylic acid is present in about 15 to 35 weight percent, making theionomer a high modulus ionomer. In a high spin embodiment, the coverincludes an ionomer where an acid is present in about 10 to 15 weightpercent and includes a softening comonomer.

The cover preferably includes a polyurethane composition comprising thereaction product of at least one polyisocyanate, polyol, and at leastone curing agent.

Any polyisocyanate available to one of ordinary skill in the art issuitable for use according to the invention. Exemplary polyisocyanatesinclude, but are not limited to, 4,4′-diphenylmethane diisocyanate(“MDI”), polymeric MDI, carbodiimide-modified liquid MDI,4,4′-dicyclohexylmethane diisocyanate (“H₁₂MDI”), p-phenylenediisocyanate (“PPDI”), toluene diisocyanate (“TDI”),3,3′-dimethyl-4,4′-biphenylene diisocyanate (“TODI”),isophoronediisocyanate (“IPDI”), hexamethylene diisocyanate (“HDI”),naphthalene diisocyanate (“NDI”); xylene diisocyanate (“XDI”);para-tetramethylxylene diisocyanate (“p-TMXDI”); meta-tetramethylxylenediisocyanate (“m-TMXDI”); ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; cyclohexyldiisocyanate; 1,6-hexamethylene-diisocyanate (“HDI”);dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5- trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of2,4,4-trimethyl-1,6-hexane diisocyanate (“TMDI”), tetracenediisocyanate, napthalene diisocyanate, anthracene diisocyanate, andmixtures thereof. Polyisocyanates are known to those of ordinary skillin the art as having more than one isocyanate group, e.g., di-, tri-,and tetra-isocyanate. Preferably, the polyisocyanate includes MDI, PPDI,TDI, or a mixture thereof, and more preferably, the polyisocyanateincludes MDI. It should be understood that, as used herein, the term“MDI” includes 4,4′-diphenylmethane diisocyanate, polymeric MDI,carbodiimide-modified liquid MDI, and mixtures thereof and,additionally, that the diisocyanate employed may be “low free monomer,”understood by one of ordinary skill in the art to have lower levels of“free” monomer isocyanate groups, typically less than about 0.1% freemonomer groups. Examples of “low free monomer” diisocyanates include,but are not limited to Low Free Monomer MDI, Low Free Monomer TDI, andLow Free Monomer PPDI.

The at least one polyisocyanate should have less than about 14%unreacted NCO groups. Preferably, the at least one polyisocyanate has nogreater than about 7.5% NCO, more preferably, between about 2.5% andabout 7.5%, and most preferably, between about 4% to about 6.5%.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol, more preferably thosepolyols that have the generic structure:

where R₁ and R₂ are straight or branched hydrocarbon chains, eachcontaining from 1 to about 20 carbon atoms, and n ranges from 1 to about45. Examples include, but are not limited to, polytetramethylene etherglycol (“PTMEG”), polyethylene propylene glycol, polyoxypropyleneglycol, and mixtures thereof. The hydrocarbon chain can have saturatedor unsaturated bonds and substituted or unsubstituted aromatic andcyclic groups. Preferably, the polyol of the present invention includesPTMEG.

In another embodiment, polyester polyols are included in thepolyurethane material of the invention. Preferred polyester polyols havethe generic structure:

where R₁ and R₂ are straight or branched hydrocarbon chains, eachcontaining from 1 to about 20 carbon atoms, and n ranges from 1 to about25. Suitable polyester polyols include, but are not limited to,polyethylene adipate glycol, polybutylene adipate glycol, polyethylenepropylene adipate glycol, ortho-phthalate-1,6-hexanediol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bonds,or substituted or unsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in thematerials of the invention. Preferably, any polycaprolactone polyolshave the generic structure:

where R₁ is a straight chain or branched hydrocarbon chain containingfrom 1 to about 20 carbon atoms, and n is the chain length and rangesfrom 1 to about 20. Suitable polycaprolactone polyols include, but arenot limited to, 1,6-hexanediol-initiated polycaprolactone, diethyleneglycol initiated polycaprolactone, trimethylol propane initiatedpolycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, the polycarbonate polyols are included in thepolyurethane material of the invention. Preferably, any polycarbonatepolyols have the generic structure:

where R₁ is predominantly bisphenol A units -(p-C₆H₄)—C(CH₃)₂-(p-C₆H₄)—or derivatives thereof, and n is the chain length and ranges from 1 toabout 20. Suitable polycarbonates include, but are not limited to,polyphthalate carbonate. The hydrocarbon chain can have saturated orunsaturated bonds, or substituted or unsubstituted aromatic and cyclicgroups. In one embodiment, the molecular weight of the polyol is fromabout 200 to about 4000.

Polyamine curatives are also suitable for use in the polyurethanecomposition of the invention and have been found to improve cut, shear,and impact resistance of the resultant balls. Preferred polyaminecuratives include, but are not limited to,3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenylmethane; p,p′-methylene dianiline (“MDA”); m-phenylenediamine (“MPDA”);4,4′-methylene-bis-(2-chloroaniline) (“MOCA”);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof, such as ETHACURE 300, commercially available fromAlbermarle Corporation of Baton Rouge, La. Suitable polyamine curatives,which include both primary and secondary amines, preferably havemolecular weights ranging from about 64 to about 2000.

Other suitable polyamine curatives include those having the generalformula:

where n and m each separately have values of 0, 1, 2, or 3, and where Yis 1,2-cyclohexyl, 1,3-cyclohexyl, 1,4-cyclohexyl, ortho-phenylene,meta-phenylene, or para-phenylene, or a combination thereof. Preferably,n and m, each separately, have values of 0, 1, or 2, and preferably, 1or 2.

At least one of a diol, triol, tetraol, or hydroxy-terminated curativesmay be added to the aforementioned polyurethane composition. Suitablediol, triol, and tetraol groups include ethylene glycol; diethyleneglycol; polyethylene glycol; propylene glycol; polypropylene glycol;lower molecular weight polytetramethylene ether glycol;1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl) ether; and mixtures thereof. Preferredhydroxy-terminated curatives include ethylene glycol; diethylene glycol;1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol, trimethylol propane,and mixtures thereof.

Preferably, the hydroxy-terminated curatives have molecular weightsranging from about 48 to 2000. It should be understood that molecularweight, as used herein, is the absolute weight average molecular weightand would be understood as such by one of ordinary skill in the art.Other suitable hydroxy-terminated curatives have the following generalchemical structure:

where n and m each separately have values of 0, 1, 2, or 3, and where Xis ortho-phenylene, meta-phenylene, para-phenylene, 1,2-cyclohexyl,1,3-cyclohexyl, or 1,4-cyclohexyl, or mixtures thereof. Preferably, nand m each separately have values of 0, 1, or 2, and more preferably, 1or 2.

Both the hydroxy-terminated and amine curatives can include one or moresaturated, unsaturated, aromatic, and cyclic groups. Additionally, thehydroxy-terminated and amine curatives can include one or more halogengroups. The polyurethane composition can be formed with a blend ormixture of curing agents. If desired, however, the polyurethanecomposition may be formed with a single curing agent.

Any method known to one of ordinary skill in the art may be used tocombine the polyisocyanate, polyol, and curing agent of the presentinvention. One commonly employed method, known in the art as a one-shotmethod, involves concurrent mixing of the polyisocyanate, polyol, andcuring agent. This method results in a mixture that is inhomogenous(more random) and affords the manufacturer less control over themolecular structure of the resultant composition. A preferred method ofmixing is known as a prepolymer method. In this method, thepolyisocyanate and the polyol are mixed separately prior to addition ofthe curing agent. This method affords a more homogeneous mixtureresulting in a more consistent polymer composition.

An optional filler component may be chosen to impart additional densityto blends of the previously described components. The selection of suchfiller(s) is dependent upon the type of golf ball desired (i.e.,one-piece, two-piece multi-component, or wound). Examples of usefulfillers include zinc oxide, barium sulfate, calcium oxide, calciumcarbonate and silica, as well as the other well known correspondingsalts and oxides thereof. Additives, such as nanoparticles, glassspheres, and various metals, such as titanium and tungsten, can be addedto the polyurethane compositions of the present invention, in amounts asneeded, for their well-known purposes. Additional components which canbe added to the polyurethane composition include UV stabilizers andother dyes, as well as optical brighteners and fluorescent pigments anddyes. Such additional ingredients may be added in any amounts that willachieve their desired purpose.

Due to the very thin nature, it has been found by the present inventionthat the use of a castable, reactive material, which is applied in afluid form, makes it possible to obtain very thin outer cover layers ongolf balls. Specifically, it has been found that castable, reactiveliquids, which react to form a urethane elastomer material, providedesirable very thin outer cover layers.

The castable, reactive liquid employed to form the urethane elastomermaterial can be applied over the inner core using a variety ofapplication techniques such as spraying, dipping, spin coating, or flowcoating methods which are well known in the art. An example of asuitable coating technique is that which is disclosed in U.S. Pat. No.5,733,428, filed May 2, 1995 entitled “Method And Apparatus For FormingPolyurethane Cover On A Golf Ball”, the disclosure of which is herebyincorporated by reference in its entirety in the present application.

The cover is preferably formed around the coated core by mixing andintroducing the material in the mold halves. It is important that theviscosity be measured over time, so that the subsequent steps of fillingeach mold half, introducing the core into one half and closing the moldcan be properly timed for accomplishing centering of the core coverhalves fusion and achieving overall uniformity. Suitable viscosity rangeof the curing urethane mix for introducing cores into the mold halves isdetermined to be approximately between about 2,000 cP and about 30,000cP, with the preferred range of about 8,000 cP to about 15,000 cP.

To start the cover formation, mixing of the prepolymer and curative isaccomplished in motorized mixer including mixing head by feeding throughlines metered amounts of curative and prepolymer. Top preheated moldhalves are filled and placed in fixture units using pins moving intoholes in each mold. After the reacting materials have resided in topmold halves for about 50 to about 80 seconds, a core is lowered at acontrolled speed into the gelling reacting mixture. At a later time, abottom mold half or a series of bottom mold halves have similar mixtureamounts introduced into the cavity.

A ball cup holds the ball core through reduced pressure (or partialvacuum) in the hose. Upon location of the coated core in the halves ofthe mold after gelling for about 50 to about 80 seconds, the vacuum isreleased allowing core to be released. The mold halves, with core andsolidified cover half thereon, are removed from the centering fixtureunit, inverted and mated with other mold halves which, at an appropriatetime earlier, have had a selected quantity of reacting polyurethaneprepolymer and curing agent introduced therein to commence gelling.

Similarly, U.S. Pat. No. 5,006,297 to Brown et al. and U.S. Pat. No.5,334,673 to Wu both also disclose suitable molding techniques which maybe utilized to apply the castable reactive liquids employed in thepresent invention. The disclosures of these patents are herebyincorporated by reference in their entirety. However, the method of theinvention is not limited to the use of these techniques.

Depending on the desired properties, balls prepared according to theinvention can exhibit substantially the same or higher resilience, orcoefficient of restitution (“COR”), with a decrease in compression ormodulus, compared to balls of conventional construction. Additionally,balls prepared according to the invention can also exhibit substantiallyhigher resilience, or COR, without an increase in compression, comparedto balls of conventional construction. Another measure of thisresilience is the “loss tangent,” or tan δ, which is obtained whenmeasuring the dynamic stiffness of an object. Loss tangent andterminology relating to such dynamic properties is typically describedaccording to ASTM D4092-90. Thus, a lower loss tangent indicates ahigher resiliency, thereby indicating a higher rebound capacity. Lowloss tangent indicates that most of the energy imparted to a golf ballfrom the club is converted to dynamic energy, i.e., launch velocity andresulting longer distance. The rigidity or compressive stiffness of agolf ball may be measured, for example, by the dynamic stiffness. Ahigher dynamic stiffness indicates a higher compressive stiffness. Toproduce golf balls having a desirable compressive stiffness, the dynamicstiffness of the crosslinked reaction product material should be lessthan about 50,000 N/m at −50° C. Preferably, the dynamic stiffnessshould be between about 10,000 and 40,000 N/m at −50° C., morepreferably, the dynamic stiffness should be between about 20,000 and30,000 N/m at −50° C.

The dynamic stiffness is similar in some ways to dynamic modulus.Dynamic stiffness is dependent on probe geometry as described herein,whereas dynamic modulus is a unique material property, independent ofgeometry. The dynamic stiffness measurement has the unique attribute ofenabling quantitative measurement of dynamic modulus and exactmeasurement of loss tangent at discrete points within a sample article.In the case of this invention, the article is a golf ball core. Thepolybutadiene reaction product preferably has a loss tangent below about0.1 at −50° C., and more preferably below about 0.07 at −50° C.

The resultant golf balls typically have a coefficient of restitution ofgreater than about 0.7, preferably greater than about 0.75, and morepreferably greater than about 0.78. The golf balls also typically havean Atti compression (which has been referred to as PGA compression inthe past) of at least about 40, preferably from about 50 to 120, andmore preferably from about 60 to 100. The golf ball polybutadienematerial of the present invention typically has a flexural modulus offrom about 500 psi to 300,000 psi, preferably from about 2000 to 200,000psi. The golf ball polybutadiene material typically has a hardness of atleast about 15 Shore A, preferably between about 30 Shore A and 80 ShoreD, more preferably between about 50 Shore A and 60 Shore D. The specificgravity is typically greater than about 0.7, preferably greater thanabout 1, for the golf ball polybutadiene material.

The center composition should comprise at least one rubber materialhaving a resilience index of at least about 40. Preferably theresilience index is at least about 50. A comparison of a number ofpolybutadiene polymers are listed in Table 1 below. Polymers thatproduce resilient golf balls and, therefore, are suitable for thepresent invention, include but are not limited to CB23, CB22, BR60, and1207G. To clarify the method of computation for resilience index, theresilience index for CB23, for example, is computed as follows:Resilience Index for CB23=100,000·[(0.954)−(0.407)]/990

Resilience Index for CB23=55 TABLE 1 Resilience Index of examplepolybutadiene polymers Tan δ at Resilience Rubber 10 cpm 1000 cpm Indexat 100° C. CB23 0.954 0.407 55 CB22 0.895 0.358 54 BR-60 0.749 0.350 40BR-40 0.841 0.446 40 Taktene 8855 0.720 0.414 31 CARIFLEX BR1220 0.4870.439 5 BUDENE 1207G 0.825 0.388 44

The molding process and composition of golf ball portions typicallyresults in a gradient of material properties. Methods employed in theprior art generally exploit hardness to quantify these gradients.Hardness is a qualitative measure of static modulus and does notrepresent the modulus of the material at the deformation ratesassociated with golf ball use, i.e., impact by a club. As is well knownto one skilled in the art of polymer science, the time-temperaturesuperposition principle may be used to emulate alternative deformationrates. For golf ball portions including polybutadiene, a 1-Hzoscillation at temperatures between 0° C. and −50° C. are believed to bequalitatively equivalent to golf ball impact rates. Therefore,measurement of loss tangent and dynamic stiffness at 0° C. to −50° C.may be used to accurately anticipate golf ball performance, preferablyat temperatures between about −20° C. and −50° C.

Additionally, the unvulcanized rubber, such as polybutadiene, in golfballs prepared according to the invention typically has a Mooneyviscosity of between about 40 and about 80, more preferably, betweenabout 45 and about 60, and most preferably, between about 45 and about55. Mooney viscosity is typically measured according to ASTM D-1646.

When golf balls are prepared according to the invention, they typicallywill have dimple coverage greater than about 60 percent, preferablygreater than about 65 percent, and more preferably greater than about 75percent. The flexural modulus of the cover on the golf balls, asmeasured by ASTM method D6272-98, Procedure B, is typically greater thanabout 500 psi, and is preferably from about 500 psi to 150,000 psi. Asdiscussed herein, the outer cover layer is preferably formed from arelatively soft polyurethane material. In particular, the material ofthe outer cover layer should have a material hardness, as measured byASTM-2240, between about 30 and about 60 Shore D, preferably from about35 to about 55 Shore D. The inner cover layer, if present, preferablyhas a material hardness from about 50 to about 75 Shore D, preferablyfrom about 60 to about 65 Shore D.

EXAMPLES

A variety of cores were prepared according to the present invention, aswell as some cores prepared using conventional materials. All cores inTable 2 were prepared to a diameter of 1.58 inches. The recipes for eachcore, and values measured for compression and COR are presented in Table2 below: TABLE 2 Golf Ball Core Properties from Various RubberFormulations Mooney viscosity Ingredients @ 100° C. 1 2 3 4 5 CB23 51100 CB22 63 100 BR-60 60 100 Taktene 8855 48 100 CARIFLEX BR1220 43 100zinc diacrylate 28 28 28 28 28 peroxide 0.53 0.53 0.53 0.53 0.53 zincoxide 4.3 4.3 4.3 4.3 4.3 tungsten 11.0 11.0 11.0 11.0 11.0 CoreProperties compression 77 75 77 76 71 COR @ 125 ft/s 0.815 0.811 0.8100.807 0.802

A variety of metal sulfide cis-to-trans catalysts that successfullyconverted a portion of the cis-polybutadiene isomer to the trans-isomerare presented in Table 3. CARIFLEX BR1220 polybutadiene (100 phr) wasreacted with zinc oxide (5 phr), dicumyl peroxide (3 phr, the freeradical initiator), and zinc diacrylate (25 phr), to form the reactionproduct as described in the present invention.

Trans-isomer conversion percentages range from below 8 percent to above17 percent for the various catalysts that are present in amounts rangingfrom below 1.7 phr to above 3.7 phr. The table clearly demonstrates theeffectiveness of numerous different cis-to-trans catalysts, at varyingconcentrations, for increasing the trans-polybutadiene content.

Example 1 A Core Prepared from According to the Invention Employing anOrganosulfur Cis-to-Trans Catalyst

A core according to the present invention was created employing anorganosulfur compound as the cis-to-trans conversion catalyst. Theresultant core properties clearly demonstrate the advantages of a golfball core made according to the current invention as compared to examplecores constructed with conventional technology. The components andphysical characteristics are presented in Table 4.

The compressive load of cores prepared according to the invention isapproximately half of the compressive load of cores constructed inaccordance with U.S. Pat. No. 5,697,856, U.S. Pat. No. 5,252,652, andU.S. Pat. No. 4,692,497, while at the same time retaining roughly thesame, and in some cases higher, COR (resilience). The core madeaccording to the current invention has a lower compressive load (soft),yet is resilient (fast). The compressive load is greater than that of acore constructed in accordance with U.S. Pat. No. 3,239,228, but has asignificantly higher COR. The core of U.S. Pat. No. 3,239,228 is verysoft and very slow (very low COR).

The percent change in dynamic stiffness from 0° C. to −50° C. was alsomeasured at both the edge and center of the cores. The dynamic stiffnessat both the edge and the center of the core of the current inventionvaried only slightly, less than 20 percent, over the temperature rangeinvestigated. The core made according to U.S. Pat. No. 3,239,228 variedover 230 percent, whereas the cores made according to other conventionaltechnology, had a dynamic stiffness that varied by greater than 130percent, and typically by as much as 150 percent, over the sametemperature range.

The percent of trans-conversion was also measured at both the center andedge of the core prepared according to the current invention, and forcores prepared as disclosed in the same four patents mentioned above,allowing a trans-gradient to be calculated. The core according to thecurrent invention had a trans-gradient of about 32 percent from edge tocenter. For the core prepared according to the current invention, thepre- and post-cure trans-percentages was also measured to determine theeffectiveness of that process. The percentage of polybutadiene convertedto the trans- isomer ranged from almost 40 percent at the center togreater than 55 percent at the edge. Two of the cores prepared accordingto conventional technology, U.S. Pat. No. 3,239,228 and U.S. Pat. No.4,692,497, had a zero trans-gradient. A third core, prepared accordingto U.S. Pat. No. 5,697,856, had only a slight trans-gradient, less than18 percent from edge to center. A fourth core, prepared according toU.S. Pat. No. 5,252,652, had a very large gradient, almost 65 percentfrom edge to center. TABLE 3 Metal Sulfide Conversion Examples CARIFLEXBR1220 100 100 100 100 100 100 100 100 100 100 100 100 100 Zinc oxide 55 5 5 5 5 5 5 5 5 5 5 5 Dicumyl peroxide 3 3 3 3 3 3 3 3 3 3 3 3 3 ZincDiacrylate 25 25 25 25 25 25 25 25 25 25 25 25 25 Cis-to-Trans“Catalyst” FeS 2.87 MnS 2.65 TiS₂ 1.70 CaS 2.20 CoS 2.77 MoS₂ 2.43 WS₂3.77 Cu₂S 4.65 SeS₂ 2.19 Y₂S₃ 2.76 ZnS 2.97 Sb₂S₃ 3.45 Bi₂S₃ 5.22 %Trans BR isomer 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5Precure % Trans BR isomer 10.5 16.1 17.0 8.3 10.3 10.1 9.2 5.8 5.2 10.210.1 10.7 10.5 Postcure

TABLE 4 Examples of Golf Balls Examples of Conventional Golf Balls ofthe Invention US#5816944 US#4971329 #1 #2 #3 US#3239228 US#5697856US#5252652 US#4692497 Chemical Constituents Polybutadiene (Shell,CARIFLEX BR1220) 100 100 100 N/A N/A N/A Polybutadiene (Firestone, 35NF) 100 N/A N/A N/A DMDS 2.1 N/A N/A N/A Carbon Black (RA) 15 N/A N/AN/A Wood Flour 24 N/A N/A N/A Sulfur 24 N/A N/A N/A Stearic Acid 1.5 N/AN/A N/A Reogen 15 N/A N/A N/A Vanox MBPC 2 N/A N/A N/A Triethanolamine 4N/A N/A N/A Zinc oxide 5 5 5 5 N/A N/A N/A Dicumyl peroxide 3 1.9 2 N/AN/A N/A Zinc Diacrylate 25 25 25 N/A N/A N/A Cis-Trans “Catalyst” N/AN/A N/A MnS 0.82 N/A N/A N/A Ditolyldisulfide 2.5 1.5 N/A N/A N/A Cu₂S 1N/A N/A N/A Resultant Core Properties Load(lbs) @10.8% Deflection 1.580″core 165.5 191.4 191.8 61.1 325 390 480 Coefficient of Restitution @125ft/s 0.783 0.777 0.785 0.599 0.779 0.805 0.775 Hardness Shore C Surface61 76 62 35 75 80 80.5 Center 52 52 59 30 70 61 66.5 Dynamic Stiffness @0° C. (N/m) Edge* 25338 27676 28493 8312 62757 83032 72235 Center 2078317390 27579 8361 61071 26264 50612 Dynamic Stiffness @ −50° C. (N/m)Edge* 30265 34523 34455 19394 92763 109053 108242 Center 23022 2060332195 18617 89677 28808 83183 Dynamic Stiffness Ratio at −50° C./0° C.Edge* 119% 125% 121% 233% 148% 131% 150% Center 111% 118% 117% 223% 147%110% 164% Loss Tangent 0° C. Edge* 0.024 0.027 0.024 0.074 0.039 0.0370.045 Center 0.025 0.023 0.023 0.073 0.033 0.025 0.043 Loss Tangent −50°C. Edge* 0.098 0.084 0.097 0.183 0.142 0.119 0.099 Center 0.067 0.0710.085 0.180 0.129 0.059 0.095 % Trans BR isomer Precure 1.5 1.5 1.5 50N/A N/A N/A % Trans BR isomer Postcure Surface 55.8 8.4 45.5 50 30.224.6 1.5 Center 37.8 4.6 25.5 50 24.7 8.5 1.5 % Trans Variation (Surf. −Center)/Surf.  32%  45%  44%  0%  18%  65%  0%*Edge is measured approximately 5 mm from the exterior surface of themeasured article.

Example 2 A Core Prepared from According to the Invention Employing anInorganic Sulfide Cis-to-trans Catalyst

A core according to the present invention was created employing aninorganic sulfide compound as the cis-to-trans conversion catalyst. Theresultant core properties clearly demonstrate the advantages of a golfball core made according to the current invention as compared to examplecores constructed with conventional technology. The components andphysical characteristics are presented in Table 4.

The compressive load is approximately half of the compressive load ofthree cores constructed in accordance with U.S. Pat. No.5,697,856, U.S.Pat. No.5,252,652, and U.S. Pat. No.4,692,497, while at the same timeretaining roughly the same, and in some cases, a higher COR(resilience). The core made according to the current invention is soft,yet resilient (fast). The compressive load is greater than a coreconstructed in accordance with U.S. Pat. No. 3,239,228, but has asignificantly higher COR. The core of U.S. Pat. No. 3,239,228 is verysoft and very slow (low COR).

The percent change in dynamic stiffness from 0° C. to −50° C. was alsomeasured at both the edge and center of the cores. The dynamic stiffnessat both the edge and the center of the core of the current inventionvaried only slightly, less than 125 percent, over the temperature rangeinvestigated. The core made according to U.S. Pat. No. 3,239,228 variedover 230 percent, whereas the cores made according to other conventionaltechnology, had a dynamic stiffness that varied by greater than 130percent, and typically by as much as 150 percent, over the sametemperature range.

The percent of trans- conversion was also measured at both the centerand edge of the core prepared according to the current invention, andfor cores prepared according to the same four patents mentioned above,allowing a trans-gradient to be calculated. The core according to thecurrent invention had a trans-gradient of about 45 percent from edge tocenter. Two of the cores prepared in accordance with U.S. Pat. No.3,239,228 and U.S. Pat. No. 4,692,497 had a zero trans-gradient. A thirdcore, prepared in accordance with U.S. Pat. No. 5,697,856, had only aslight trans-gradient, less than 18 percent from edge to center. Afourth core, prepared in accordance with U.S. Pat. No. 5,252,652, had avery large gradient, almost 65 percent, from edge to center.

Example 3 A Core Prepared from According to the Invention, Employing aBlend of Organosulfur and Inorganic Sulfide Cis-to-trans Catalyst

A core according to the present invention was created employing a blendof organosulfur and inorganic sulfide compounds as the cis-to-transconversion catalyst. The resultant core properties clearly demonstratethe advantages of a golf ball core made according to the currentinvention as compared to example cores constructed with conventionaltechnology. The components and physical characteristics are presented inTable 4.

The compressive load is approximately half of the compressive load ofthree cores constructed in accordance with U.S. Pat. No. 5,697,856, U.S.Pat. No. 5,252,652, and U.S. Pat. No. 4,692,497, while at the same timeretaining roughly the same, and in some cases a higher COR (resilience).The core made according to the current invention is soft, yet resilient(fast). The compressive load of the invention is greater than a fourthcore constructed in accordance with U.S. Pat. No. 3,239,228, but has asignificantly higher COR. The core constructed in accordance with U.S.Pat. No. 3,239,228 is very soft and very slow (low COR).

The percent change in dynamic stiffness from 0° C. to −50° C. was alsomeasured at both the edge and center of the cores. The dynamic stiffnessat both the edge and the center of the core of the current inventionvaried only slightly, less than 121 percent, over the temperature rangeinvestigated. The core made in accordance with U.S. Pat. No. 3,239,228varied over 230 percent, whereas the cores made according to otherconventional technology had a dynamic stiffness that varied by greaterthan 130 percent, and typically by as much as 150 percent, over the sametemperature range.

The percent of trans-conversion was also measured at both the center andedge of the core prepared according to the current invention, and forcores prepared to the same four patents mentioned above, allowing atrans-gradient to be calculated. The core according to the currentinvention had a trans-gradient that about 44 percent from edge tocenter. For the core prepared according to the current invention, thepre- and post-cure trans-percentages was also measured to determine theeffectiveness of that process. The percentage of polybutadiene convertedto the trans-isomer ranged from almost 26 percent at the center togreater than 45 percent at the edge. Two of the cores prepared inaccordance with U.S. Pat. No. 3,239,228 and U.S. Pat. No. 4,692,497 hada zero trans-gradient. A third core prepared in accordance with U.S.Pat. No. 5,697,856 had only a slight trans-gradient, less than 18percent from edge to center. A fourth core, prepared in accordance withU.S. Pat. No. 5,252,652 had a very large gradient, almost 65 percentfrom edge to center.

Example 4 Comparison of a Conventional Dual Core Ball to Dual Core BallPrepared According to the Invention

A dual core golf ball according to the present invention was createdhaving a solid center, an intermediate layer surrounding the solidcenter, and a multilayer cover disposed concentrically around theintermediate layer. The components and physical characteristics arepresented below in Table 5. TABLE 5 Example 4: Dual Core CenterComposition CARIFLEX BR1220 100 zinc diacrylate 20 dicumyl peroxide 2.5zinc oxide 39 DTDS 0.75 Center Properties % trans Precure 1.5 % transPostcure 40 load in lbs required (10.8% deflection) 109 MantleComposition CB23 80 zinc diacrylate 38 VAROX 231 XL 0.42 DBDB-60 0.15zinc oxide 6 polyisoprene 20 Inner Cover Composition and Properties NaSURLYN 50 Li SURLYN 50 Shore D hardness 68 thickness 0.03 in Outer CoverComposition and Properties MDI polyurethane thickness 0.03 in

A solid center was constructed for the ball of the present invention.The center was created from CARIFLEX BR-1220 polybutadiene as thestarting material, the only difference being replacing the VAROX802-40KE-HP peroxide (conventional technology) with a DTDS cis-to-transcatalyst of the current invention and dicumyl peroxide. Thissubstitution allows a portion of the polybutadiene material to beconverted to the trans-configuration during the molding process. Theresulting solid center had an outside diameter of approximately 1.15inches. The polybutadiene reaction product prepared thereby had atrans-isomer content of 40 percent compared to the 1.5 percenttrans-isomer of conventional balls. An intermediate layer, havingoutside diameter of approximately 1.56 inches, was constructed aroundthe solid center to form a core. The outer layer is made of CB23 havinga molecular weight of about 360,000 and a Mooney viscosity of about 51.

Examples 5-8 Comparison of Conventional Golf Balls with Those PreparedAccording to the Invention

A polybutadiene reaction product was prepared for two conventional priorart compositions (Examples 5-6) as well as one prepared according to theinvention (Examples 7-8). The recipes for each composition can be seenin Table 6 below. TABLE 6 Example 5 Example 6 Example 7 Example 8 (phr)(phr) (phr) (phr) Reaction Product CARIFLEX BR1220 100 100 100 100 zincoxide 26.6 2.67 26.6 26.6 barium sulfate — 31 — — zinc diacrylate 2022.3 20 20 dicumyl peroxide 2 — 2 2 VAROX 802 40KE-HP^(a) — 0.89 — —polymeric sulfur 0 0 0.25 0 elemental sulfur 0 0 0 0.25 pre-cure trans-1.5% 1.5% 1.5% 1.5% polybutadiene content Golf Ball Core post-curetrans- 1.5% 1.5%  12%  12% polybutadiene content in reaction productAtti Compression 53 23 26 21 COR n/a^(b) 0.72 0.77 0.76^(a)A di-(2-t-butylisopropylperoxy)-benzene peroxide commerciallyavailable from R. T. Vanderbilt of Norwalk, CT.^(b)The core of Example 5 was sufficiently rigid to crack during testingof the coefficient of restitution, indicating an undesirably low COR.

These constituents were mixed and molded, thereby converting apercentage of cis-to a trans-conformation, in a solid sphere sized likethe core of a golf ball. Examples 7-8 illustrate the significantconversion of cis-polybutadiene to trans-polybutadiene when a sulfurcis-to-trans catalyst is present according to the invention compared tothe lack of conversion in Examples 5-6 when no sulfur catalyst ispresent. Moreover, Examples 7-8 illustrate the improved coefficient ofrestitution with no significant change in compression that can beachieved with golf balls including the reaction product according to theinvention.

The invention described and claimed herein is not to be limited in scopeby the specific embodiments herein disclosed, since these embodimentsare intended as illustrations of several aspects of the invention. Anyequivalent embodiments are intended to be within the scope of thisinvention. Indeed, various modifications of the invention in addition tothose shown and described herein will become apparent to those skilledin the art from the foregoing description. Such modifications are alsointended to fall within the scope of the appended claims.

1. A golf ball comprising: a center formed of a reaction productcomprising: polybutadiene; a crosslinking material; a free radicalsource; a cis-to-trans catalyst present in an amount sufficient toproduce a reaction product comprising at least about 32 percenttrans-polybutadiene, wherein the reaction product has a percent changein dynamic stiffness from 0° C. to −50° C. of less than 125 percent; anda cover comprising a thermoplastic or thermoset polyurethane.
 2. Thegolf ball of claim 1, wherein the percent change in dynamic stiffness isless than 121 percent.
 3. The golf ball of claim 1, wherein themolecular weight of the polybutadiene is about 200,000 or greater. 4.The golf ball of claim 3, wherein the molecular weight of thepolybutadiene is about 300,000 to about 500,000.
 5. The golf ball ofclaim 1, wherein the crosslinking material is present in an amount ofabout 10 to about 40 parts per hundred of the reaction product.
 6. Thegolf ball of claim 1, wherein the cis-to-trans catalyst comprises atleast one of an organosulfur compound, an aromatic organic compound, ora mixture thereof.
 7. The golf ball of claim 6, wherein the organosulfurcompound comprises metal.
 8. The golf ball of claim 6, wherein theorganosulfur compound is substantially free of metal.
 9. The golf ballof claim 6, wherein the aromatic organic compound comprises a hydroxygroup, a metal salt of a hydroxyl, a mercapto group, a metal salt of amercapto group, a carboxy group, a metal salt of a carboxyl, anacrylate, a metal salt of an acrylate, or a combination thereof.
 10. Thegolf ball of claim 6, wherein the aromatic organic compound issubstantially free of metal.
 11. A golf ball comprising: a center formedof a reaction product having a first dynamic stiffness at −50° C. lessthan about 130 percent of a second dynamic stiffness at 0° C., whereinthe reaction product comprises: polybutadiene; a crosslinking material;a free radical source; a cis-to-trans catalyst present in an amountsufficient to produce a reaction product comprising at least about 32percent trans-polybutadiene isomer; and a cover comprising a castablereactive liquid material.
 12. The golf ball of claim 10, wherein thefirst dynamic stiffness is less than about 125 percent of the seconddynamic stiffness.
 13. The golf ball of claim 11, wherein the firstdynamic stiffness is less than about 110 percent of the second dynamicstiffness.
 14. The golf ball of claim 10, wherein the castable reactiveliquid material comprises polyurethane.
 15. The golf ball of claim 10,wherein the crosslinking material is present in an amount of about 10 toabout 40 parts per hundred of the polybutadiene.
 16. A golf ballcomprising a center formed of a reaction product having a first dynamicstiffness at −50° C. less than about 130 percent of a second dynamicstiffness at 0° C., wherein the reaction product comprises:polybutadiene having a molecular weight of greater than about 200,000; acrosslinking material; a free radical source; a cis-to-trans catalystcomprising a metal-containing organosulfur compound; and a covercomprising a thermoset or thermoplastic polyurethane.
 17. The golf ballof claim 16, wherein the cis-to-trans catalyst is present in an amountsufficient to produce a reaction product comprising about 32 percent orgreater trans-polybutadiene isomer.
 18. The golf ball of claim 17,wherein the metal-containing organosulfur compound comprises cadmium,copper, lead, and tellurium analogs of diethyldithiocarbamate, cadmium,copper, lead, and tellurium analogs of diamyldithiocarbamate, cadmium,copper, lead, and tellurium analogs of dimethyldithiocarbamate, ormixtures thereof.
 19. The golf ball of claim 16, wherein the molecularweight of the polybutadiene is about 300,000 to about 500,000.
 20. Thegolf ball of claim 16, wherein the golf ball comprises an inner coverlayer disposed between the center and the cover, wherein the inner coverlayer comprises an ionomer resin, a polyurethane, a polyetherester, apolyetheramide, a polyester, a dynamically vulcanized elastomer, afunctionalized styrene butadiene elastomer, a metallocene polymer,nylon, acrylonitrile butadiene-styrene copolymer, or blends thereof.